Carburizing



Patented (jet. 10, 1956 UNITED STATES VPATENT y 2,525,700 OFFICE 2,525,? CABBURIZING George K. Manning, Philip C. Rosenthal, and George P. Krumlauf, Columbus, Ohio, assignors to Battelle Memorial Institute, Columbus, Ohio, a corporation of Ohio No Drawing. Application December 3, 1943, Serial No. 512,834

(Cl. DIS-30) 1 Claim.

penetration but also the maximum carbon concentration in the carburized material. The depth of penetration usually can be rather easily controlled by varying the time and temperature of the carburizing cycle. The rate of penetration is also somewhat dependent upon the time and temperature of the carburizing cycle and, in addition, can be affected somewhat by the addition of certain energizers to the carburizing medium. The maximum carbon concentration in the carburized case is, however, not susceptible to such ready control.

Solid commercial carburizers commonly result in cases having maximum carbon concentrations ranging upward from 0.90 per cent carbon. In many commercial applications such high carbon concentrations, in excess of 0.90 per cent, are regarded as an advantage. This is particularly true when high abrasion resistance is required.

On the other hand, in numerous applications abrasion resistance is of little or no importance and high surface hardness is the principal requirement. The hardness of a carburized case does not increase proportionately as the maxi mum carbon content increases in the higher ranges. In fact, as is discussed by Burns, Moore,

and Archer, Transactions of American Society for Metals, volume XXVI, 1938, page 14, the maximum hardness curve levels off at about 0.50 per cent carbon and further increases in this element do not increase the hardness appreciably. However, although the hardness does not increase, the ductility and the toughness of the case continue to decrease as the carbon content is increased. Therefore, in order to obtain a case with the best combination of hardness and toughness, a maximum carbon concentration substantially less than 0.90 per cent, and in many instances preferably about 0.50 per cent, is often desired.

The best combination of hardness and toughness is desired in many applications. As typical examples, gears, camshafts, pinions, bearings,

and face-hardened armor plate may be mentioned, In the production of face-hardened armor, for example, considerable difficulty is often encountered during the straightening operation. The low ductility and toughness of the case structure, resulting from the relatively high carbon content of the case, causes considerable loss in production because of breakage. For this reason it is extremely important to restrict the maximum carbon content of the ,case

of the face-hardened armor to the lowest level commensurate with satisfactory hardness,

thereby obtaining the maximum practical dutility and hardness in the case. In this particular application, a further advantage is obtained inasmuch as increased case ductility tends to improve the ballistic resistance of the armor.

One way that these relatively low carbon cases M may be obtained is by a diffusion period following the carburizing period. In gas carburizing, this can be accomplished without too much difficulty by proportioning the carburizing and inert gases of the mixture so that the carburizing and diffusion steps either occur simultaneously or follow ,eachother. The main disadvantage in this procedure is the additional furnace time required. on the other hand, in pack carburizing using a solid compound, the problem is not so readily solved and two separate cycles are required. The process becomes quite costly, therefore, both because of the double handling and because of the additional furnace time required.

,A further method of restricting the maximum carbon content of the case has been proposed. It has been suggested that the addition of ferrosilicon, or of certain other silicon-containing materials, to a standard commercial carburizer is effective in limiting the maximum carbon content of the case produced in a single carburizing treatment. The addition of approximately 20 per cent of rinelyground ferrosilicon to the carburiz ing compound tends to eliminate from the case the hypereutectoid zones, that is those zones coni taining, in excessof about 0.85 to 0.95 per cent carbondepending upon the composition of the base materiali With this treatment, however, a substantial portion of the case is of eutectoid composition; containing an average of from about 0.85 to 0.95 per cent carbon in most instances. Althoughsuch cases may be used for certain applications, for example, idler shafts and other surfaces requiring high abrasion resistance;

there are numerous other applications, such as roller bearings, piston pins, transmission gears, camshafts, machine gun ejector parts, and armor plate, where it may be particularly desirable to limit the maximum carbon content of the case to the hypoeutectoid range, that is, containing less than about 0.85 to 0.95 per cent carbon. As has been mentioned previously, in some instances particular advantages may be gained by restricting the carbon content of the case to a maximum value as low as 0.50 per cent or even lower.

It is therefore one object of our invention to provide an improved method for regulating the carbonconcentration within the case: of car burized material.

Another object of this invention is to provide a carburizing compound that is capable of yielding a case having an essentially hypoeutectoid structure.

A further object of our invention is to develop a process for limiting the maximum carbon concentration in a carburized case to a value less than: about 0.85 per cent and preferably to any 3 desired carbon content within the range of from about 0.45 to about 0.75 per cent.

Yet a further object of this invention is to regulate the carbon concentration at or near the surface of carburized material in a predictable manner without resorting to .a ,difiusion treatment.

Still another object of our invention is to provide an improved method for the production of face-hardened armor having a superior combination of hardness and toughness or ductility in the carburized case.

Other and further objects of this invention Will be apparent from the following description and theappended claims.

We have discovered that the maximum carbon content of a carburized case may be appreciably lowered to within the hypoeutectoid range Without double handling and in less time than is required for both a carburizing and diffusion treatment by the use of a carburizing compound composed essentially of a varying amount of a metallic chloride, hereinafter referred to as chloride, and a silicon-containing material and a carbonaceous base. With a carburizing compound of this type, a case with a. low maximum carbon content can be obtained and that maximum can be controlled and predetermined by proper choice of the amount and kind of chlorides and silicon-containing materials used with the carburizing compound.

In general, we have found a total chloride addition of from about 0.5 to about 15 per cent is effective; however, we prefer to add from about 2 to about 8 per cent. Although additions in excess of 15 per cent may be used, the additional benefits obtained are not commensurate with the increased costs. As previousl mentioned, the inhibiting effect obtained depends upon the nature of the chloride as well as upon the quantity and nature of the silicon-bearing material employed. By varying the chloride content Within the limits mentioned, we have found it possible to obtain maximum carbon concentrations ranging from a value of about 0.40 per cent up to that normally developed by the use of the untreated carburizer.

The addition of'from about 2 to about 25 per cent of silicon as a silicon-containing material is desirable; however,' we prefer to add from about 5 to about 15 per cent of silicon as a sili con-bearing agent. Additions in excess of per cent may be made; however, the dilution efiect tends to become excessive when too much is added. The particle size of the silicon-containing material has an effect upon the results produced. In general, the effectiveness of the silicon addition increases as the particle size of the material is decreased. For most purposes, the best results are obtained in the use of ferrosilicon and calcium silicide when the material is finer than 80-mesh; with siliconcarbide, We prefer to use a particle size at least 100-mesh or finer.

The desirable results obtained by means of the form of their carbonateswas used on the "carbonaceous base. This 'carburizer gives a relatively low carbon content by itself. Additions of chlorides and silicon-containing materials, in accordance with our invention,' wereadded't this base. A carburizing cycle consisting of holding for 24 hours at 1700 F. was used. The carbon concentrations were determined by analyzing turnings from successive layers. The first layer from each sample Was 0.002-inch thick; the second, 0.003 inch thick; and the next three layers, 0.005 inch thick. Eight additionallayer's', each 0.010 inch thick, were then turned from the specimen. The maximum carbon concentration Was usuall found in the 0002 inch thick layer.

Table I shows the eifecto'f the addition of various amounts of several different chlorides on the maximum carbon content of the carburized case. As is shown by this table, the maximum carbon content of the case decreases progressively as increasing amounts of nickel chloride,

' chromium chloride, or combinations of the tWo are added to a carburizing compound containing,

in addition, a silicon-containing material. For

example, the'addition'of 8 percent'nickcl chlo ride and 15 per cent silicon carbide to a car} burizer that normally givesa "maximum carbon content of 0.95 per cent, results in a caseihaving a maximum carbon content of 0.43 per cent.

TABLE I Efiect of various chloride additions on maximum carbon content of the ca burzaed case Composition of Carburizing Compound, Per Cent mum Specimen NO. Ohloridcs Silicon s-flicn $53521 t t Added As (-Earbuon Per cent 100 0.95 10 84 0.78 10 83 0.73 10 81 0.53 10 77 V 0.43 10 84 0.86 10 83 0.81 10 81 0.65 B-CICla 10 77 0. 62 %-NiClz,}-CrCl3 10 84 0. 78 1-NiClz,l-CrCl l0 7 83 0.69 Z-NiClfl-OrOla 10 "81 0.66 2-NaC1 7 84' 0.06 4-NaCl 7 82 0.89 6-NaO1 7 0. 64 8-NaCl 7 78 0. 74 4-CllC12 10 81 0.74 4-Oa012 l0 76 0. 62

7 As is also shown by Table I, the addition of 2 or 6 per cent of sodium chloride is more effective than an addition of 4 or 8 per cent of the same material. There is also a tendency toward pitting of the surface of the case when sodium chloride additions of 6 per cent or more are used. This pitting effect is not found when other chlorides are used. 1

For a given concentration, nickel chloride ranks high in its inhibiting effect while barium chloride, for example, is much less effective. As a general rule, the most effective chlorides are those TABLE II mum carbon content of the carburized case Composition of Carburizing Compound, Per Cent Maxi- Specimen No. Commum Chlorides Silicon menial S35E55 Added As- Carburizer Per cent 100 0.95 1 94 ,0. 91 3. 91 0. 80 7 86 0. 61 81 0.53 12 76 0. 62 21 66 0.47 3. 5 89 0.82 7 82 0.54 10 76 0.45 3.3 90. 5 0.86 6.6 85 0.78 10 79.5 0.78 10 76 0. 74 7 88. 2 0.84

TABLE I11 Efiect of chloride and silicon-containing additions when made singly Composition of Carburizing Compound, Per Cent Maxi- Specimen N0. Commum Carbon Silicon incrcial Chlorides Silicon Added Catbw Content rizer Per cent 1 100 0.95 47-.. 2-NiC1z,2-ClC1 96 1.12 85 0.87 86 0. 85 1 80 0. 88

1 Carburizer diluted with MgO.

having a boiling point in excess of the carburizing temperature.

Table II shows the effect of the addition of varitends to vary progressively with increases in silicon additions. From the data in Tables I and II it is apparent that, for an addition equivalent to 10 per cent of silicon, ferrosilicon is slightly more effective than silicon carbide, while silicon carbide is somewhat more effective than silica or calcium silicide. However, even silica is an effective silicon-bearing addition as is indicated by the fact that the addition of 4 per cent calcium chloride and 20 per cent silica flour reduced the maximum ous amounts of different silicon-bearing materials. With a given chloride addition, the reduction in the maximum carbon content of the case carbon content of the resulting case from 0.95 to 0.62 per cent.

The necessity of adding both a chloride and a silicon-containing material is clearly shown by the data in Table HI. It is interesting to note that chloride additions, in the absence of a sili- The carburizing compound of this invention may be prepared in any suitable manner; however, we have found the following method to be highly desirable: A carbonaceous base, preferably an energized commercial carburizer, is thoroughly mixed with the desired amount of silicon-containing material. The required amount of chloride is then dissolved in a suitable binder, such as molasses water, and the resulting solution added to the dr mixture. The whole is then thoroughly 7 commonuse, while a temperature around 1700 F. is usually preferred. Although the time at carburlzillg temperature affects the depth of the case, it has relatively small effect upon the maximum carbon concentration. For example, specimens carburized in a compound containing 2 per cent nickel chloride, 2 per cent chromium chloride, 15 per cent silicon carbide, and, the balance commercial carburizer, for periods of 4, 8, 1 1, 16, and 24 hours, had cases with maximum carbon concentrations of 0.67, 0.60, 0.68, 0.58, and 0.60 per cent respectively.

It is possible to reuse the mixture by merely replacing that which is consumed and that which is lost by dusting and by drag-out. In one test;

the same mixture was reused five times. After each cycle, the compound was passed over a N0. screen and the fines discarded. Twenty-five per cent ,of the weight of the remaining coarse particles was added as fresh mixture after each of the first four cycles and eleven per cent after the fifth cycle. The results indicated a rather abrupt decrease in maximum carbon content between the second and third cycle. Thereafter, no conspicuous change occurred.

The above examples are given merely to illustrate the principles, compositions, and methods of our invention, and it willbe understood that variations are possible within the scope of the appended claims.

Unless otherwise specified, all percentages referred to herein will be understood to represent percentages by weight rather than by volume.

From the foregoing description of our invention, it will be apparent that we have provided a novel carburizing agent that is capable of producing, in a single-treatment process, carburized cases having maximum carbon concentrations,

substantially below those produced by the car burizing processes known heretofore. This highly desirable effect is obtained by the incorporation of a combination of one or more chlorides and a silicon-containing material in an essentially standard carburizer. Although neither chlorides nor silicon-containing materials are suitable for the purposes hereindisclosed when added alone, the addition of the two in combination results in a marked reduction in the maximum carbon concentration of a case produced by a normal carburizing cycle.

Having thus described our invention, What we claim is:

A carburizing compound having a base composed of an energized carburizing material and containing in addition, about 2 per cent nickel chloride, about 2 per cent chromium chloride, and about 15 per cent silicon carbide.

GEORGE K. MANNING. PHILIP C. ROSENTHAL. GEORGE P. KRUMLAUF.

REFERENCES (JITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 787,926 Lecarme Apr. 26, 1905 1,076,453 ROdman Oct. 21, 1913 1,310,918 Mebame July 22, 1919 1,593,132 Nelson July 20, 1926 1,921,367 Mohin Aug. 3, 1933 2,149,7 l7 Redman Mar. 7, 1939 2,188,063 Solakian Jan. 23, 1940 2,249,581 Solakian July 15, 1941 2,263,906 Solakian Nov. 25, 1941 2,320,872 Kramer et al. June 1, 1943 FOREIGN PATENTS Number Country Date 3,586 Great Britain of 1893 25,986 Great Britain of 1903 Certificate of Correction Patent No. 2,525,700 October 10, 1950 GEORGE K. MANNING ET AL.

It is hereby certified that error appears in the printed specification of the above numbered patent requiring correction as follows:

, Column 5, lines 67 to 69, inclusive, beginning With the syllable ous strike out all to and including the WOICl case in line 69, and insert the same before tends in line 57 same column;

and that the said Letters Patent should be read as corrected above, so that the same may conform to the record of the case in the Patent Oflice. Signed and sealed this 16th day of January, A. Dr. 1951.

a THOMAS F. MURPHY,

\ Assistant G'ommz'ssz'oner of Patents. 

